Ziyarah of the Prophet and invocations at his grave

Imam Sadiq (a.s.) said: Before proceeding to Medina or prior to entering it, perform Ghusl. Then proceed to the grave of Allah’s Messenger (s.a.w.s.) and salute him. Go to the pillar located on the right by the head of the grave. Stand there with your left shoulder towards the grave, your right shoulder towards the pulpit of the Prophet and face the Qibla, this being the closest location to the head of the Prophet. Then recite:
I bear witness that there is no god but Allah; He is alone and has no partners and I bear witness that Muhammad (s.a.w.s.) is His servant and messenger. I bear witness that you are Allah’s Messenger (s.a.w.s.) and you are Muhammad, son of Abdullah. I bear witness that you announced the messages of your Lord, you advised your Ummah, you fought with wisdom and by giving good counsel until death came to you. You fulfilled your obligations, you were kind to believers and harsh to disbelievers. Hence Allah granted you the highest honored position of the honored ones. Praise to be Allah who, through you, saved us from polytheism and deviation. O Allah! Convey Your blessings, blessings of Your proximate angels, blessings of Your righteous servants, blessings of Your prophet messengers, blessings of all the inhabitants of heavens and earths and blessings of everyone from first to last who sanctifies the Lord of the Worlds, on Muhammad (s.a.w.s.), Your servant, Your Messenger, Your Prophet, Your trustee, Your confidant, Your beloved, Your chosen one, Your special servant and the best of Your creation. O Allah! You said, “And had they, when they were unjust to themselves, come to you and asked forgiveness of Allah and the Apostle had (also) asked forgiveness for them, they would have found Allah Oft-returning (to mercy), Merciful.”(4:64) And I have come to Your Prophet, repenting and begging forgiveness for my sins and I have turned to You through Your Prophet, the Prophet of Mercy, Muhammad (s.a.w.s.). O Muhammad (s.a.w.s.)! I have turned to Allah, Your Lord and mine, through you, so that He forgives my sins.
Imam (a.s.) continued: If you have a request, face Qibla keeping your back to the grave; raise your hands and ask for your request; it will be granted, Insha Allah.

Reference: 
Kamiluz Ziyaraat By: Ibne Quluwayh
Translated by: Sayyid Athar Husain S. H. Rizvi